The present invention generally relates to a recording optical system used in a laser beam printer, a digital copy machine and so on, and more particularly to a recording optical system capable of changing the spot size of a light beam.
Conventionally, in order to carry out, high quality printing, a laser beam recording apparatus which is capable of recording a gradational image has been proposed. In this type of laser beam recording apparatus, due to changing the dot size for a pixel, the gradational image is obtained.
In Japanese Laid-Open Patent Application No. 61-an aperture stop by which the dot size of the laser beam is changed and a control means for controlling the size of the aperture stop are disclosed.
In Japanese Laid-Open Patent Application No. 63-296069, an apparatus in which the intensity of a light beam emitted from a semiconductor laser element is controlled so that the dot size of the light beam is changed is disclosed. In this apparatus, when the image information of two adjacent dots corresponds to a case where the light beam is not irradiated, the dot size is enlarged so that it is possible to prevent a line image from separating .
In the apparatus disclosed in Japanese Laid-Open Patent Application No. 61-113018, the mechanical aperture stop, a liquid crystal aperture stop or the like is used as the aperture stop so that the response of the aperture stop is slow. Thus it is difficult to rapidly print.
In the apparatus disclosed in Japanese Laid-Open Patent Application No. 63-296069, the intensity of light beam emitted from the semiconductor laser is changed so that it is difficult to sufficiently change the dot size of the light beam.